Individuals with Parkinson's disease (PD) suffer from tremor, bradykinesia and rigidity. Over time, their postural control becomes impaired, and their overall neuronal and physical function degenerates. One contributory factor to this functional decline is reduced muscle strength that is caused partly by the disease, and partly by reduced physical activity. Medication and deep brain stimulation compensate for the neuronal changes caused by the disease but have negative side effects, and do not compensate for reduced physical activity. The central hypothesis of this application is that progressive resistance exercise will improve neuromuscular function, and hence the signs and symptoms of PD. In order to test this hypothesis, 50 subjects with PD will take part in a randomized, control, blinded study of exercise. Twenty-five subjects will be randomly assigned to receive progressive resistance training. Twenty-five subjects will be randomly assigned to a Fitness Counts program that has been developed by the National Parkinson Foundation. It is a low intensity program based primarily on stretching, flexibility and non-progressive strengthening. Twenty- five neurologically healthy subjects will also be tested to provide normative data. Both groups of subjects with PD will be evaluated at baseline, and every six months over the two-year period. The hypotheses in Aims 1 through 4 will be tested at six months. Aim 1 tests the hypothesis that progressive resistance exercise will demonstrate a greater reduction in the motor section of the Unified Parkinson's Disease Rating Scale than Fitness Counts. Aim 2 tests the hypothesis that in comparison to Fitness Counts, progressive resistance exercise will exhibit greater improvements in: i) muscle strength, 2) reducing the amount of action tremor, 3) reducing the amount of time required to release a muscle contraction, 4) improving measures of agonist and antagonist muscle activation during movement, and 5) increasing movement speed. Aim 3 tests the hypothesis that, in comparison to Fitness Counts, progressive resistance exercise will exhibit greater improvements in function as measured through: i) increases in the Berg Balance Scale, 2) increases in normal walking velocity, 3) decreases in double limb support time, 4) increases in the distance walked in six minutes, and 5) increases in the score on the Physical Performance Test. Aim 4 tests the hypothesis that in comparison to Fitness Counts, progressive resistance exercise will exhibit a greater improvement in the quality of life of patients with PD as measured by the Parkinson's Disease Questionnaire (PDQ-39). Aim 5 tests the hypothesis that the progressive resistance group will show a statistically significant improvement in the motor UPDRS and other dependent measures at 24 months in comparison with the Fitness Counts group. The results of the proposed studies will advance the understanding of how progressive resistance exercise affects the control of movement, overall physical function, and quality of life in individuals with PD.